Thank you for the explanation. Ken Rockwell on his web seems to indicate that by downsampling in post processing, the noise get eliminated effectively the same as if you had a lower MP camera. So my question is:
1. Is his statement correct ? 2. By setting up camera at smaller JPEG size (ie 4256 x 2832), is it the same effect as if I was down sampling (resizing) in post processing in Photoshop or aperture.
If both these are correct, then D800 sounds like a winner and I do not understand why people complain about high MP/High noise as you can have the best of both worlds 1) low noise if you choose to downsample (used in low light situations) 2) high detail when you do need it (ie landscape pictures)...
under 11 February 2012, Saturday - D800 Changes the Game
Ken Rockwell: "Some people are afraid that the D800 won't look good at high ISOs. Au contraire, if you look at my Nikon D3X versus Nikon D3 ISO comparison, what common men seem to forget is that at a given ISO and print size, the two are the same! In fact, the noise is the same, while the D3X image still has more resolution at ISO 6,400. The D3X and its higher resolution wins big time over the D3 and D700, but at $8,000, Nikon can keep them.
Having more pixels allows you the choice of ultra-resolution for huge prints or crops, and when displayed at reasonable print or screen sizes, the natural downsampling gives the same noise advantage of having fewer, larger pixel wells. If you've got three times as many pixels, the noise cancels the same way it does when you have larger wells, so it's a non-issue. The D800 will work great at high ISOs!
While less experienced people might worry, the key here is that having more pixels than you need is a very good thing, because it gives you options. You can't shoot a D700 at 36 MP, but at the same ISO and resolution, the D800 ought to smoke the old D700."